Hydrocephalus is the most common cause of abnormally
large heads in newborns. It is a result of Ventricular
enlargement with excessive Cerebrospinal Fluid (CSF.) It
occurs when CSF production exceeds reabsorbtion; it is
usually due to obstruction in the normal pathway of its pathways
within the Brain. Most often it is due to narrowing or
obstruction of the Aqueduct of Sylvius (also called the
"Cerebral Aqueduct"), but may be due to obstruction at
the CSF outlet passages of the 4th Ventricle (The "outlets are known
as the Foramina of Luschka and Magendie.) Another cause may lie
in the CSF reabsorbtion pathways surrounding the Brain Stem and
Cerebral Hemispheres called the Subarachnoid Spaces. Blood
in the Subarachnoid Space (from hemorrhage from any cause)
or infection (a condition called Meningitis)
may cause scar formation within the Subarachnoid Space and
obstruction of CSF flow within this Space.

Figure 1: Diagram of the Ventricular System

Classification of Hydrocephalus & Relationship to Cause

Hydrocephalus is classified according to whether the obstruction
to CSF flow lies within the Ventricular System (Non-communicating
Hydrocephalus) or outside the system in the Subarachnoid Space
(Communicating Hydrocephalus).

Communicating Hydrocephalus occurs when CSF flows
freely into the Subarachnoid Space but encounters an obstruction
to its flow pattern or reabsorbtion in the Subarachnoid Space.
The "obstruction" may be "complete" (as happens in acute extensive
hemorrhage or extensive infection in the subarachnoid Space) although
it is usually "incomplete" which results in a differential rate
between CSF production and CSF reabsorbtion. The consequence is a
relative excess production of CSF which increases the pressure within
the Ventricular System much like what happens when a child's balloon
is inflated. Communicating Hydrocephalus is most often
secondary to meningeal inflammation from infection or blood in the
Subarachnoid Space.

Non-communicating Hydrocephalus occurs as a result of a
blockage of the CSF pathway at some point within
the Ventricular system. This may be due to "Atresia"
(failure to develop) of the Cerebral Aqueduct, tumors within the
Ventricular System (such as
Meningioma,
Ependymoma,
Medulloblastoma,
Choroid Plexus Papilloma).

Figure 2A (Left): MRI Scan (Gadolinium Enhanced Sagittal View)
4th Ventricular Medulloblastoma (Curved Arrow) in a
young child fills the Ventricle, compresses the Brain Stem and
the Cerebellum as well as obstructing the CSF pathway resulting
in Obstructive Hydrocephalus. The 3rd Ventricle is
dilated as part of the Hydrocephalus (Horizontal Arrow.)

"Megalencephaly" is another condition presenting with an
abnormally large and malfunctioning Brain.

DIAGNOSIS

Neuroimaging

Neuroimaging evaluation in newborns can include Cranial
Ultrasound, CT scan, or MRI scan. Cranial imaging
may show separation of sutures, areas of thinning
of the bones, or intracranial calcifications
(which are often associated with congenital infections).
Among the disease entities that must be considered as potential causes
of Hydrocephalus are intracranial "space-occupying" lesions
(such as Subdural Hematoma, Porencephalic Cyst, Tumor, etc.),
all of which can be identified by CT scan. CT shows the
Ventricular size and possibly the site of
obstruction.

Plain skull films may show a "beaten-metal" appearance of
the bones (common in infants with
Myelomeningocoeles and
Hydrocephalus). This peculiar appearance usually indicates a
prolonged increase in intracranial pressure.

Ultrasound can define the degree of Ventricular
dilation, and serial studies can document progression of
the Hydrocephalus. Ultrasound is valuable after intraventricular
hemorrhage, since Ventricular dilation may be transient and
require only medical treatment.

Blood & CSF evaluation

When congenital infection is suspected, it is important
to consider obtaining blood serologic studies for Toxoplasma
gondii, Rubella Virus, Treponema pallidum, Herpes Virus, and
Cytomegalovirus.

Examination of the Cerebrospinal Fluid (CSF) may be the
best method to offer clues to the source of an infection.

Electroencephalogram

An electroencephalogram (EEG) may be helpful in patients who develop
"seizures (Epilepsy).

TREATMENT

Treatment depends on the actual cause.

Medical management with agents such as Diamox
(acetazolamide) and glycerol or lumbar
punctures (in cases where the Hydrocephalus is "Communicating")
to reduce the CSF pressure may offer some temporary
assistance.

Surgical management becomes important, however, when there is
progressively dilating Ventricles as documented on serial
Neuroimaging scans. This becomes critical if the head
circumference is increasing too rapidly. This operation is called a
"Shunt" procedure which is designed to reduce the
intracranial pressure. It involves creating a diversionary
pathway from the Lateral Ventricle by inserting a special catheter into
the Ventricle that is then connected to a special "one-way valve"
apparatus which, in turn, is attached to a longer, "Distal" catheter.
In most instances the Neurosurgeon will choose to place a
Ventriculo-peritoneal Shunt (rather than a
Ventriculo-atrial variety) with the "distal"
catheter being inserted into the peritoneal (abdominal)
Cavity. In this way the CSF is reabsorbed through the
lining of the peritoneal cavity into the blood stream.

Fetal surgery (conducted before birth while still within the
uterus) to treat Congenital Hydrocephalus has not been
successful.

Required Follow-up

After the shunt is placed, the infant's progress should be
followed with particular attention to the head
circumference, neurological and intellectual development.
Neurosurgeons are concerned for the increased risk of infections in
the face of an implanted "foreign body" (the Shunt system).
Periodic partial CT or ultrasound (if the Anterior
Fontanelle is still open) can be used to monitor Ventricular
size.

While it is recognized that some children may develop to a point where
they cease to need the shunt, the determination of this is quite
difficult. In most patients it is preferable to leave the shunt in
place.